This invention relates to a radio communication device, such as a cellular phone, which is used in a code division multiple access (CDMA) system and, in particular, to a method of controlling electric power in the radio communication device so as to reduce electric power consumption in the radio communication device.
Recent attention tends to be focused on a code division multiple access (CDMA) system which enables concurrent communication by the use of the same frequency band among a plurality of stations, such as mobile stations and base stations. This is because the CDMA system is very effective in comparison with the other systems, such as FDMA (Frequency Division Multiple Access) system, IDMA (Time Division Multiple Access) system, in the view of efficiently utilizing a frequency source. In other words, the CDMA system has high frequency utilization efficiency as compared with the FDMA system, the TDMA system.
However, the CDMA system is disadvantageous in that it is larger in power consumption of a receiver than the FDMA and the TDMA systems and, in particular, becomes large in the power consumption in a standby state or mode of the receiver in the CDMA system.
Herein, it is to be noted that proposals have been offered about a wide variety of the CDMA systems each of which adopts individual power saving methods. For example, Japanese Unexamined Patent Publication No. Hei 9-261172, namely, 261172/1997, (will be called Reference 1 hereinafter) has disclosed a CDMA-TDD (Time Division Duplex) system which comprises a plurality of base stations and a plurality of mobile communication devices or terminals. In addition, a mobile communication control station is also included in the CDMA-TDD system to control the base stations. More specifically, a dummy signal is transmitted from each mobile terminal to the base station during non-transmission at a low power level, as compared with a usual transmission power level. In this event, the base station selects a transmission antenna by using the dummy signal received by the base station under control of the mobile communication control station.
Such a mobile communication control station is peculiar to the CDMA-TDD system and is therefore not applicable to the other CDMA systems. This is because a specific station must be prepared in the CDMA-TDD system mentioned in Reference 1.
In Japanese Unexamined Patent Publication, No. Hei 10-209943, namely, 209943/1998 (will be referred to as Reference 2), an intermittent mode in a standby state is divided into a first intermittent mode and a second intermittent mode so as to reduce power consumption in the standby state. More specifically, the first intermittent mode may be a usual intermittent mode of repeating an on state and an off state at a predetermined period while the second intermittent mode serves as a power saving mode which has a period longer than the predetermined period. Accordingly, it is possible with this method to save power in the second intermittent mode in comparison with the first intermittent mode. Thus, the method can save power in the standby state by switching the first and the intermittent modes from one to another.
However, a radio communication device, such as a cellular phone, which is operable in accordance with the above-mentioned method must switch not only the first and the second intermittent modes but also must automatically and frequently execute hand-off operation. Therefore, it is difficult to apply the above-mentioned method to a radio communication device of the CDMA system.
Alternatively, disclosure has been also made in Japanese Unexamined Publication No. Hei 9-261167, namely, 261167/1997 (will be called Reference 3) about a system which has a base station side for transmitting a speech channel for speech and a paging channel which has a narrow band in comparison with the speech channel to call a mobile station or radio terminal. On the other hand, the mobile terminal has a wide-band A/D converter put into an inactive state in a standby state and a narrow-band A/D converter operated in the standby state to receive the paging channel. With this mobile station, the narrow-band A/D converter alone is operated in the standby state with the wide-band A/D converter kept inactive. In other words, electric power may be supplied only to the narrow-band A/D converter and a portion corresponding to the narrow-band A/D converter in the standby state. Accordingly, the power can be saved in the standby state in the mobile station.
However, the mobile station must have the narrow-band A/D converter in addition to the wide-band A/D converter and becomes inevitably complex in structure. Moreover, this system needs to prepare, on a transmission side, not only a spread code for spreading the speech channel but also another spread code for spreading the paging channel. This means that both the base station and the mobile station should be changed in structure. Furthermore, it is to be noted that the method disclosed in Reference 3 can reduce the electric power in the standby state but can not reduce the electric power in the communication state.